This invention relates generally to clean room wipes, and to methods for preparing and using such wipes, so as to reduce or eliminate the possible spontaneous combustion of wipes after contacting chemicals often found in clean rooms. Specifically, our invention relates to wipes used in a xe2x80x9cclean roomxe2x80x9d, semiconductor fabrication plants, metal-plating plants and in other applications and environments to clean up alkaline (caustic) spills and contaminants.
Clean rooms are being used in a growing variety of industrial processes, especially processes such as semiconductor fabrication processes, where there are very stringent requirements for maintaining cleanliness.
Contamination, even by bits of lint or dust, can bridge these circuits and cause such devices to be defective and is a major source of rejection. Particles and contaminants, even the smallest particles and contaminants, are frequently many times larger than feature sizes in the individual transistors and diodes in microelectronic devices. Any such particles and other contaminants present during the semiconductor fabrication can cause serious functionality and reliability problems in the final manufactured devices.
Therefore, there is a need to maintain all surfaces as free from such contamination as possible. This is usually accomplished in part by wiping these surfaces, and a number of specialized wipers have been developed for this purpose. However, the wiper itself, in addition to being able to wipe cleanly, should not contribute to the problem of dust.
Clean room products, for example wipes, gloves, gowns, tools, electronic components, filters, and reactants, must be designed and manufactured to avoid contamination. Clean room wipes used in sensitive areas, such as semiconductor fabrication clean rooms and pharmaceutical manufacturing facilities, must be carefully selected for characteristics such as particle emission levels, levels of ionic contaminants, adsorptiveness, resistance to attack or degradation by wear or exposure to cleaning materials, and lack of attack by or degradation by biocides, among other factors.
Stringent clean room requirements have been met by the provision of specially fabricated products. These products include xe2x80x9capplicatorsxe2x80x9d and xe2x80x9cwipesxe2x80x9d. These products are designed to emit very few loose particles or ions, while maintaining structural integrity when used. One example is a wipe described in EP0336 661 A2 to Paley et al. Other examples of such applicators or wipes and their method of manufacturing are described in U.S. Pat. No. 5,271,995 to Paley et al. and U.S. Pat. No. 5,227,844 to Bhattacharjee et al., the disclosures of which are incorporated herein by reference.
The contamination which is to be controlled is often called xe2x80x9cmicrocontaminationxe2x80x9d because it consists of small physical contaminants, such as particulate matter of a size between that of bacteria and viruses, and chemical contaminants in very low quantities, typically expressed in parts per million or parts per billion. Clean room levels define acceptable levels of contaminants by size. Clean room levels are indicated in Table 1.
During normal manufacturing and maintenance operations within the clean rooms used for integrated circuit manufacturing, pharmaceutical manufacturing, and metal plating operations, there are many situations when structural surfaces must be wiped clean with either dry or saturated wipes to remove particles, ions, or chemical contamination.
Like particulates, chemical spills within clean rooms and metal plating plants are also a major concern. These chemicals will release chemical vapors, droplets (particles), and can cause corrosive damage to equipment, personnel and integrated circuit products.
During the fabrication of semiconductor devices numerous corrosive and/or reactive chemicals must be used. Very often there are chemical spills during chemical transfers to the baths or automated equipment. Such spills can also take place during the transfer of wafer boats between different tanks. Many times there are also chemical spills down the side of the containers that must be removed. These chemicals can be very hazardous to personnel, equipment and the semiconductor devices if not properly controlled.
During the metal plating operations there can be spills of corrosive and strong oxidizing solutions. These solutions are hazardous to the personnel and can also be a significant fire hazard.
Normally these chemical spills are composed of mineral acids, aromatic solvents, ketones, alcohols, amines (NMP) and alkanolamines (monoethanol amine, diglycol amine, etc.). Metal plating operations may have caustic or organic solvent based chemistries with various metal ions in different oxidized states. Wipes that are dry or saturated with water or isopropyl alcohol have heretofore been used to clean up these chemical spills.
Recently a new class of chemicals has become very important in the manufacturing of the IC devices. This class of chemicals contains hydroxylamine and hydroxylamine compounds mixed in a variety of amine and alkanolamines. The pHs of these solutions are usually between 9 to 11.5. These chemistries have proved to be very effective because of the unique reductive power of the hydroxylamine compounds. Examples of such chemistries are in such patents as U.S. Pat. Nos. 5,279,771, 5,381,807, and 5,482,566.
Prudent practices when wiping up hydroxylamine should include quenching the wipe in water before disposal. However, clean room personnel can not always be relied upon to quench these wipes. One potential problem is that when these chemistries are spilled and need to be wiped up the hydroxylamine will react with various ions and oxygen and will undergo autocatalytic oxidation. There is also the potential for an exothermic reaction between the wipe materials and the contaminant, and resulting spontaneous combustion, especially from alkaline chemistries such as hydroxylamine-based formulas. These reactions can generate thermal energy and under certain conditions can generate enough heat to allow the wipes to smolder and generate smoke and steam.
Many times clean room personnel have not adequately quenched the wipes and the spontaneous combustion has taken place.
Metal plating solutions will also have chemicals in different oxidation states that need to be neutralized to reduce the possible spontaneous combustion problems.
It is an object of the present invention to solve or alleviate the foregoing problems. Accordingly, it is an object of the invention to produce clean room products, particularly clean room wipes that can neutralize chemical spills, particularly those spills containing hydroxylamine compounds. In particular, it is an object of the invention to provide clean room wipes which can also neutralize amines, hydroxylamine, and alkanolamine, without degradation of the clean room quality of the products. It is a further object of the present invention to provide such clean room products saturated with acids that can neutralize these amines, alkanolamines and hydroxylamine and which are relatively simple to use. This invention is not intended to neutralize caustic based cyanide plating solutions, since there may be a release of the deadly hydrogen cyanide gas if the wipes of this invention were to be used for that purpose. The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
The wipes of our invention have an absorbent substrate containing at least one organic acid. The acid is capable of reacting with and neutralizing caustic in spilled chemicals. The absorbent substrate can be of any type known in the art to be useful for clean rooms, that is, a substrate that has stringent limits on dust and lint generation, and that is able to hold at least about 50 percent of its weight in liquids. The absorbent substrate may be a knitted, woven, and nonwoven fabrics.
The acid is an organic acid. Clean room environments often can not be exposed to concentrated ions such as would be found in a mineral acid. It is preferred that the acid or acids have an ionization constant, pKa, at 27xc2x0 Centigrade, greater than 1.2, and a vapor pressure of less than 7 kPascal at 27xc2x0 Centigrade. It is preferred that the acid or acids be a liquid at room temperature.
Examples of a monobasic acid include formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, and butyric acid. Examples of a dibasic acid include ascorbic acid, gluconic acid, malic acid, malonic acid, oxalic acid, succinic acid, and tartaric acid. Examples of a tribasic acid include citric acid and gallic acid. The preferred acids have from 1 to 7 carbon atoms and more than one carboxylic group per molecule.
A crystallization inhibitor is beneficially present to inhibit the formation of acid crystals which may be a source of dust. The crystallization inhibitor includes the solvent, and may include a co-solvent, for example a surfactant, an alcohol, a glycol, or a mixture thereof. Preferably the co-solvent has from 3 to 6 carbon atoms, more preferably from 3 to 4 carbon atoms.
The wipe is beneficially stored in a substantially air tight pouch, so that the wipe does not dry out or attract dust during handling and storage. The package or pouch may be made of a polyolefin selected from the group consisting of polyethylene, polypropylene, polybutene, poly(4-methylpentene-1), copolymers of propylene and ethylene, copolymers of ethylene and vinyl acetate, copolymers of ethylene and ethyl acrylate, and copolymers of ethylene and acrylic or methacrylic acid. The package has a thickness of from 0.5 to 10 mils.
The invention also includes a method of cleaning up caustic chemicals, particularly wherein the contaminants are amines, alkanolamines, and hydroxylamines. The method includes contacting the spilled chemical with the wipe and blotting up the spill. The wipe is then disposed of, without necessarily rinsing or quenching the wipe in water.
The invention also includes a method of cleaning up caustic chemicals in clean rooms. The method includes contacting the spilled chemical with the wipe and blotting up the spill. The wipe is then disposed of, without necessarily rinsing or quenching the wipe in water, but preferably in a sealed container.